Multiple evolutionary pathways to decreased lateral plate coverage in freshwater threespine sticklebacks.

Area of Science:

• Evolutionary biology
• Genetics
• Ecology

Background:

• Adaptation to new environments relies on genetic variation or new mutations.
• When specific genetic variations are absent, alternative functional solutions drive adaptation.
• The ectodysplasin-a (Eda) gene is crucial for threespine stickleback lateral plate development.

Purpose of the Study:

• Investigate adaptation mechanisms in threespine sticklebacks colonizing freshwater.
• Examine the role of genetic variation in the ectodysplasin-a (Eda) gene and plate morphology.
• Determine if alternative functional solutions evolve under genetic constraints.

Main Methods:

• Studied phenotypic and genetic variation in plate number and size.
• Compared five marine and six freshwater threespine stickleback populations.
• Assessed the frequency of alleles associated with reduced plate number in the Eda gene.

Main Results:

• Freshwater sticklebacks reduced plate size, not number, when Eda gene variation was limited.
• A distinct "small-plated" morph was identified as dominant in some northern European freshwater populations.
• This small-plated morph appears functionally equivalent to the low-plated morph.

Conclusions:

• Convergent evolution can lead to functional similarity through different genetic pathways.
• Genetic constraints can drive the evolution of alternative adaptive strategies.
• The small-plated morph represents a novel adaptation to freshwater environments in threespine sticklebacks.